This invention is related to boat motors, and primarily, but not necessarily limited to, outboard motors. More specifically, the invention relates to a flow device which not only protects the propeller blades of a boat motor, but also enhances the performance of the motor itself by increasing efficiency.
There have been previous attempts to provide devices which protect boat propellers and/or enhance performance by directing or confining flow in the area of the propeller in a rearward direction. In this regard, attention is directed to U.S. Pat. Nos. 4,680,017; 4,428,735; 3,658,028; 3,099,240; 2,963,000; French Pat. No. 1,543,181; and Canadian Pat. No. 509,171.
However, the prior art devices are often difficult to install by reason of their rigid and generally solid cylindrical configuration, or otherwise complex construction. The present invention represents an improvement over such prior art devices in that it is of relatively simple construction and characterized by ease of installation and removal. The invention effectively protects the propeller from trash, debris, rocks and the like, which could otherwise cause significant damage. At the same time, the invention increases the efficiency of the motor which, in turn, enhances the motor's overall performance characteristics.
In the present invention, an elongated open-ended, i.e., tubular, shroud is provided for enclosing the propeller of an outboard boat motor. The shroud is formed in two half-sections, hinged together about an axis lying on the periphery of the shroud and extending parallel to both the longitudinal axis of the shroud, and the axis of rotation of the propeller. In the preferred embodiment, a piano-type hinge extends from the forward to rearward end of the shroud, interrupted only by a relatively short elongated slot designed to receive the motor housing skeg as explained more fully below.
The hinge is located on the bottom, or lower, peripheral portion of the shroud (the "bottom" in the context of this invention referring to the lowermost portion of the shroud, when in position about the propeller of a generally upright motor). Thus, it will be appreciated that the half-sections may be pivoted "upwardly" to a "closed" position completely surrounding the propeller, such that the longitudinal axis of the shroud is substantially coincident with the axis of rotation of the propeller.
The half-sections of the shroud are also provided with one or more fastener-type elements so that, after the shroud halves have been closed about the propeller, they may be clamped together by nuts and bolts, screws, or the like. The closed shroud has a generally cylindrical configuration, although it is preferably tapered slightly, front-to-rear, so that the diameter of the shroud at the inlet or forward end is larger than the diameter of the shroud at the outlet or rearward end. The shroud, whether or not tapered, confines flow in a substantially linear direction, thereby increasing efficiency by preventing radial dissipation of a portion of the energy generated by the propeller. The tapered configuration further ensures that, when the boat is traveling in a forward direction, a solid body of water exits the shroud at increased velocity, due to a venturi effect established at the rearward end of the shroud.
Substantially open grills are provided for the forward and rearward ends of the shroud or housing, each including a plurality of vertically oriented fins or rods which do not restrict flow but which are sufficient to prevent trash and other debris from entering the shroud and damaging the propeller. The vertically oriented vanes, or rods also tend to reduce turbulence by smoothing the flow entering and/or leaving the shroud.
In one exemplary embodiment, one grill is formed as a separate ring-like component which may be slipped onto one end of the closed shroud, while the other grill is formed integrally with the shroud half-sections. By this arrangement, the separable grill, once attached, serves to hold the half-section portions of the shroud together. It is contemplated, however, that even with the removable grill feature, one or more additional fasteners will be employed to secure the shroud halves in the closed position during use as previously described.
In another exemplary embodiment, the grills are formed in sections and are integral with, or permanently attached to, the respective shroud half-sections.
The flow directing device of this invention is designed to engage the boat motor housing at no fewer than three points of attachment. First, the shroud is provided with an elongate slot along the hinge, for receiving the lower tip of a skeg. The skeg is a vertically oriented fin, found on most outboard motor designs, which projects downwardly from the lowermost portion of the motor housing, below the propeller.
An upper portion of the shroud is provided with a pair of mounting plate assemblies which are designed to resiliently engage and clamp a respective pair of anti-cavitation plates which extend horizontally outwardly from either side of the housing, above the propeller. the anti-cavitation plates are designed to prevent water from being sucked, or drawn, from above and into the propeller area.
In the exemplary embodiments of this invention, the mounting plate assemblies are located adjacent the free edges of the shroud half-sections, i.e., in the closed position, a mounting plate assembly extends along a significant portions of the length of the shroud, on either side of the motor housing, just above the propeller.
Each mounting plate assembly includes a vertically oriented supporting wall and a first horizontal plate, supported by the vertical wall, which extends inwardly toward the motor housing as further explained below. A second horizontal plate is fixed to the underside of the first horizontal plate, with one elongated edge, i.e., the inward edge facing the motor housing, substantially aligned with a corresponding edge of the first horizontal plate. The first and second horizontal plates are attached at selected locations by brazing, welding or other suitable means, which nevertheless permit resilient separation of the plates along the aligned edges.
The mounting plate assemblies are mounted on the shroud, in such a way that, as the shroud half-sections are closed about the propeller, the anti-cavitation plates are wedged between the first and second horizontal plates of each mounting plate assembly. In this regard, one or both of the first and second horizontal plates of each assembly is constructed of spring steel to create a resilient gripping action on the anti-cavitation plates.
In addition to the above described points of attachment with the motor housing, additional fasteners are employed, as previously described, to clamp the shroud half-sections to each other, so that the shroud is securely and firmly attached to the motor housing, with no possibility of the shroud becoming misaligned or otherwise interfering with the operation of the motor.
Once attached to the motor, the shroud of this invention effectively prevents the propeller from coming into contact with the trash, debris, rocks or other harmful solid material. At the same time, the shroud has significant safety related aspects insofar as it prevents hand, foot, or other contact with the propeller by the boat operator or others when the motor is in the water or out. The shroud also transforms the usual turbulence associated with this type of motor into useable flow by confining and directing the flow in a front-to-back direction, to thereby improve motor efficiency. As previously noted, a preferred, tapered shroud configuration creates a venturi effect at the rearward end of the shroud, thereby increasing the flow velocity and further improving performance.
It will therefore be appreciated that the invention is characterized by significant protective, safety, performance, and ease of installation features which heretofore have been unavailable in the prior art.
While described primarily with respect to single propeller outboard motor, it will be understood that the present invention may also be adapted for use with dual propeller outboard motors as well as inboard motors. The shroud may also be adapted to fit motors of different sizes in the various categories mentioned.
Further objects and advantages of the invention will become apparent from the detailed description which follows.